Polytetrafluoroethylene (PTFE) is widely used in industrial and biomedical applications because PTFE has a number of beneficial properties. For instance, PTFE is commonly considered to be chemically inert. Because of this and other properties of PTFE, some companies in the semiconductor processing industry form PTFE into a “liner” that is used to line a bottle that is then used to store chemicals.
A liner is formed in the following manner. First, a modified PTFE powder is made into a billet, which is a filled cylinder that is compressed. The billet is baked until the particles coalesce and stick together. The billet is formed into a film through a process called skiving, which planes off a thin layer of material. The skiving process is similar to peeling an apple. The end result of the skiving process is one or more sheets of PTFE material. Each sheet is commonly called a film.
A liner is formed by “welding” portions of cleaned PTFE films to make a four-sided, two-dimensional bag with a spout called a fitment. The spout is also welded onto the liner. The liner is then used to line a polyethylene overpack, which is what gives the liner structural support, and the final product is a PTFE-lined bottle.
Chemicals are stored in the PTFE-lined bottle and removed from or placed into the bottle via the fitment. The chemicals stored in these bottles are typically ultra-pure and the PTFE liners, being chemically inert, generally do not chemically react with the stored chemicals.
Nonetheless, it has been determined that PTFE liners may cause an increase in observed particles for liquids stored in contact with the PTFE liners. For instance, pure water can be pumped into a bottle having a PTFE liner, the bottle inverted a number of times, and the pure water pumped out of the bottle. The water pumped out of the bottle is passed through a particulate counter, which counts particles in a certain size range. For conventional PTFE-lined bottles, the particle count can vary widely, as judged by the standard deviation of the particle count. Lot variability, where PTFE liners are made from different lots of PTFE films, may be partially responsible for the high standard deviation of the particle count. Moreover, the particle count tends to be relatively high, especially when it is considered that it would be beneficial for PTFE liners to cause no particle count.
Thus, conventional techniques for processing PTFE liners fail to substantially prevent relatively high particle counts and high standard deviation of those particle counts. Therefore, a need exists for improving PTFE films and liners and other products made from PTFE films.